Contact and Non-contact Forces, Effect of A Force and Units - Notes
FORCE
1A Contact and Non-contact Forces, Effect of A Force and Units
Force: A
physical cause which changes or tends to change either the size and shape of
the body or the state of rest or the state of motion of the body.
Forces are categorized into two kinds : 1.
Contact Forces
2.
Non – contact forces
1. Contact Force: The force acting between two bodies when the bodies are in physical contact. It is also
called Direct Force. The
following forces are considered contact forces.
a) Frictional Force: When a body slides or rolls over the surface of another body, a force resists the motion
of the body and acts in
the opposite direction. This is called Frictional force (Force of Friction).
b) Normal Reaction Force: When a body is placed on a surface the body exerts a force which is equal to
its weight and the surface also exerts an equal and opposite force normal to the surface.
c) Tension Force as applied through a string: When a body is suspended by a string, the body exerts a
force on the string and pulls it vertically downwards which balances the weight of the body. This force
is
called the Tension Force(T).
d) Force exerted by a spring: Restoring Force: The force exerted by a compressed or stretched spring
on an object attached to the spring.
This force is directly proportional to its elongation or compression (the displacement of the other end of
the spring).
The elongation of a spring is directly proportional to the weight suspended from it – Spring balance
works on this principle.
e) Force exerted during collision: When two bodies collide, equal and opposite forces act each body
and they push each other.
When a body A moves towards another body B and collides with it, the force exerted by A on B is called
Force of action and B exerts an equal
and opposite force on A i.e. called Force of Reaction.
2. Non-contact Forces: The Force experienced by the bodies when they are not in physical contact (Forces
at distance).
a) Gravitational Force: The force of attraction existing between any two particles in the universe due to
their masses.
The force on a body due to Earth’s attraction is called Pull of Gravity or Force of Gravity. Due to this
force an object released
from a height falls down.
b)
Electrostatic Force : The force acting between two charges when they are at a
distance .
example: A comb rubbed on a dry hair, attracts bits of paper
due to electrostatic force
c) Magnetic Force: The force existing between two magnetic poles even
when they are at a distance.
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